A Pen By
Soós Tamás

JavaScript preprocessors can help make authoring JavaScript easier and more convenient. For instance, CoffeeScript can help prevent easy-to-make mistakes and offer a cleaner syntax and Babel can bring ECMAScript 6 features to browsers that only support ECMAScript 5.

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` ````
<html>
<head>
<meta charset="utf-8"/>
<title>Recamán</title>
<link rel="stylesheet" href="style.css"/>
<script src="recaman.js"></script>
</head>
<body>
<canvas id="canvas" width="512" height="512"></canvas>
</body>
</html>
```

` ````
body {
padding: 0;
background-color: black;
}
#canvas {
width: 512px;
height: 512px;
display: block;
margin: auto;
padding: 0;
}
```

` ````
let canvas, ctx;
let width, height;
let a = [];
let n, i;
let forward;
let s;
let c1, c2;
let l;
let g;
let t;
let start;
let fancy;
function setup() {
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
width = canvas.width;
height = canvas.height;
a[0] = 1;
n = 0;
i = 1;
s = 4;
l = 10000;
c1 = "#6599FF";
c2 = "#FF9900";
g = grid(width / s, s);
fancy = true;
start = performance.now();
requestAnimationFrame(loop);
}
function loop(time) {
//Sequence
if(n-i > 0 && !a[n-i]) {
n -= i;
forward = false;
} else {
n += i;
forward = true;
}
a[n] = 1;
i += 1;
t = time - start;
g.enable(n, forward);
g.update();
//Draw
if(fancy) {
ctx.fillStyle = "black";
ctx.globalAlpha = 1;
ctx.fillRect(0,0,width, height);
}
g.draw();
if(i < l)
requestAnimationFrame(loop);
}
function grid(n, s) {
function cell(x, y, s, type=-1) {
let o = 0;
let o1 = 0.8;
let o2 = 0.95;
let ts;
let ds = 750;
let dl = 60000;
function calcOpacity(o, f) {
let r = (64*o-32)/3*Math.pow(f,4)-(128*o-96)/3*Math.pow(f,3)+(92*o-94)/3*Math.pow(f,2) -(28*o-30)/3*f+o;
if(r < 0)
r = 0;
if(r > 1)
r = 1;
return r;
}
return {
enable: function(tp) {
type = tp;
ts = t;
ds += ts / 200;
if(o1 <= 1) {
o1 += 0.2;
}
},
update: function() {
if(type != -1) {
let f = (t-ts)/ds;
if(f < 1) {
if(type == 1)
o = calcOpacity(o1*Math.abs(Math.cos(ts/dl)), f);
else if(type == 0) {
o = calcOpacity(o2*Math.abs(Math.cos(ts/dl)), f);
}
}
}
},
draw: function() {
if(type == 1) {
ctx.fillStyle = c1;
if(fancy)
ctx.globalAlpha = o;
ctx.fillRect(x, y, s, s);
} else if(type == 0) {
ctx.fillStyle = c2;
if(fancy)
ctx.globalAlpha = o;
ctx.fillRect(x, y, s, s);
}
}
}
}
function psign(n) {
return 2 * Math.floor(2 * ((n / 2) % 1)) - 1;
}
function calcPos(n) {
let f = Math.floor(Math.sqrt(n));
let ps = psign(f);
let x = n - f*f;
let pos = {x: 0, y: 0};
//Squares
pos.x = ps * Math.floor((f - 1) / 2);
pos.y = ps * Math.ceil((f - 1) / 2);
//Offset
pos.x += -ps * (Math.floor((x - 0.5) / f)*Math.floor((x - 0.5) % f) - 1);
pos.y += ps * ((Math.abs(x - (f + 1)) - (f + 1)) - (Math.floor((x - 0.5) / f)*Math.floor((x - 0.5) % f) - 1));
return pos;
}
let cells = [];
for(let i = 0; i < n; i += 1) {
for(let j = 0; j < n; j += 1) {
cells.push(cell(j*s, i*s, s));
}
}
return {
enable: function(m, type) {
//Calculate position
let center = {x: n/2, y: n/2};
let pos = calcPos(m);
if(pos.x >= -n/2 && pos.x < n/2 && pos.y >= -n/2 && pos.y < n/2)
cells[(center.y + pos.y) * n + center.x + pos.x].enable(type);
},
update: function() {
cells.forEach((c) => c.update());
},
draw: function() {
cells.forEach((c) => c.draw());
}
}
}
window.onload = setup;
```

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